Environmental sealing arrangement for furcated optical fibers

ABSTRACT

An assembly for protecting spliced optical fibers includes: a fiber optic cable comprising at least one optical fiber and a surrounding jacket; at least one elongate tubular member housing the optical fiber, wherein a gap exists between the elongate tubular member and the jacket such that the optical fiber has an exposed region; and a premold block formed of an ultra-low pressure material, the premold block encasing the exposed region of the optical fiber.

RELATED APPLICATION

This application claims the benefit of and priority from U.S.Provisional Patent Application No. 62/011,177, filed Jun. 12, 2014, thedisclosure of which is hereby incorporated herein by reference in itsentirety.

FIELD OF THE INVENTION

The present invention relates generally to optical fibers, and morespecifically to the protection of optical fibers from environmentalconditions.

BACKGROUND

In many fiber optic cable assemblies, it may be necessary to remove theouter jacket layers of the cable and expose a length of fiber that isthen inserted into a smaller diameter furcation tube. This may be donebecause a robust fiber optic cable normally has a jacket diameter thatis too large to fit into standard fiber optic connectors, whereas asmaller diameter furcation tube can fit into such connectors.Unfortunately, this transition technique leaves a gap between thefurcation tube and the cable jacket, which exposes a section of thefiber to the environment. It also breaks the continuity of strengthmembers in the cable that are designed to absorb the tensile load of theassembly rather than subjecting the fiber to the load. Similar exposureof fibers may occur when a fiber optic cable is broken out (i.e.,“furcated”) into multiple branches of fibers or subgroups of fibers,each with its own furcation tube.

One solution for covering the gap between the jacket and the singlefurcation tube utilizes a close fitting plastic tube (transition tube)that fits over the gap. Once it is in place, the transition tube isfilled with epoxy. The epoxy mechanically binds the strength membersfrom the furcation tube and the cable together to avoid having the fibercarry any tensile load. In addition, the epoxy fills the gap, therebypreventing contamination or environmental attack of the fiber. Thetransition tube and the sections of the furcation tube and cableimmediately adjacent the furcation tube are covered with a piece ofadhesive lined heat shrink tubing. During a heating process to shrinkthe heat-shrink tubing, the adhesive lining the tubing melts and forms abond between the transition tube and the inner surface of theheat-shrink tubing. The heat shrink tubing adds UV and abrasionresistance to the assembly.

Although this technique is commonly employed, it has some disadvantages.The epoxy is expensive due to its initial cost, pot life, unrecoverablewaste, and the slow rate of cure. Also, it involves a number ofdifferent components and a good deal of labor to complete. Thus, atechnique that reduces or eliminates these shortcomings may bedesirable.

SUMMARY

As a first aspect, embodiments of the invention are directed to anassembly for protecting optical fibers. The assembly comprises: a fiberoptic cable comprising at least one optical fiber and a surroundingjacket; at least one elongate tubular member housing the optical fiber,wherein a gap exists between the elongate tubular member and the jacketsuch that the optical fiber has an exposed region; and a premold blockformed of an ultra-low pressure material, the premold block encasing theexposed region of the optical fiber.

As a second aspect, embodiments of the invention are directed to anassembly, comprising: a fiber optic cable comprising at least oneoptical fiber and a surrounding jacket; an elongate tubular memberhousing the optical fiber, wherein a gap exists between the elongatetubular member and the jacket such that the optical fiber has an exposedregion; and an overmold formed of a low pressure material, the overmoldencasing the exposed region of the optical fiber.

As a third aspect, embodiments of the invention are directed to a methodfor breaking out optical fibers from a fiber optic cable. The methodcomprises the steps of:

(a) stripping a portion of a surrounding jacket from a fiber optic cablecomprising at least one optical fiber residing within the jacket;

(b) inserting the optical fiber into an elongate tubular member, whereina gap exists between the elongate tubular member and the jacket suchthat the optical fiber has an exposed region; and

(c) molding a premold block over the exposed region of the optical fiberat a molding pressure of between about 0 and 50 psi.

As a fourth aspect, embodiments of the invention are directed to amethod for transitioning optical fibers from a fiber optic cable into anelongate tubular member, comprising the steps of:

(a) stripping a portion of a surrounding jacket from a fiber optic cablecomprising at least one optical fiber residing within the jacket;

(b) inserting the optical fiber into an elongate tubular member, whereina gap exists between the elongate tubular member and the jacket suchthat the optical fiber has an exposed region; and

(c) molding an overmold over the exposed region of the optical fibers ata molding pressure of between about 50 and 800 psi.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a perspective view of a fiber optic cable being broken outinto two separate subgroups of optical fibers, wherein the subgroups offibers are housed in furcation tubes.

FIG. 2 is a perspective view of the fiber optic cable and optical fiberswithin furcation tubes of FIG. 1 covered with a protective premold blockaccording to embodiments of the invention, wherein the premold block isshown as transparent for clarity.

FIG. 3 is a perspective view of an ovemolded cover that surrounds thepremold block of FIG. 2.

FIG. 4 is a perspective view of a transition between a fiber optic cableand optical fibers within a furcation tube protected by an overmoldedcover according to embodiments of the invention.

DETAILED DESCRIPTION

The present invention is described with reference to the accompanyingdrawings, in which certain embodiments of the invention are shown. Thisinvention may, however, be embodied in many different forms and shouldnot be construed as limited to the embodiments that are pictured anddescribed herein; rather, these embodiments are provided so that thisdisclosure will be thorough and complete, and will fully convey thescope of the invention to those skilled in the art. It will also beappreciated that the embodiments disclosed herein can be combined in anyway and/or combination to provide many additional embodiments.

Unless otherwise defined, all technical and scientific terms that areused in this disclosure have the same meaning as commonly understood byone of ordinary skill in the art to which this invention belongs. Theterminology used in the below description is for the purpose ofdescribing particular embodiments only and is not intended to belimiting of the invention. As used in this disclosure, the singularforms “a”, “an” and “the” are intended to include the plural forms aswell, unless the context clearly indicates otherwise. It will also beunderstood that when an element (e.g., a device, circuit, etc.) isreferred to as being “connected” or “coupled” to another element, it canbe directly connected or coupled to the other element or interveningelements may be present. In contrast, when an element is referred to asbeing “directly connected” or “directly coupled” to another element,there are no intervening elements present.

Referring now to the figures, an exemplary transition arrangementbetween a fiber optic cable 10 and two optical fiber subgroups 12 housedwithin furcation tubes 13 is illustrated in FIG. 1. As can be seentherein, optical fibers from the fiber optic cable 10 diverge into thesubgroups 12, thereby leaving a region R of optical fibers unprotectedby a jacket or a strength member. Each of the optical fiber subgroups 12typically includes multiple fibers, but in some instances may includeonly a single optical fiber.

Referring now to FIG. 2, the region R and the ends of the fiber opticcable 10 and optical fiber subgroups 12 are shown encased within aultra-low pressure premold block 14 that is molded thereon. The premoldblock 14 is applied over the exposed fiber region R and the ends of thefiber optic cable 10 and the optical fiber subgroups 12 with extremelylow pressure (e.g., 1-50 psi), which is sufficiently low that it doesnot damage the exposed optical fibers. (Compare, for example, thetypical molding pressure from a conventional injection molding machine,which may be on the order of 1,000 to 20,000 psi). As used herein, theterm “ultra-low pressure” refers to a molding pressure of between 0 and50 psi. Once the material of the premold block 14 is cured (typically in10 seconds or so) and removed from the mold, the exposed optical fibersin the region R are protected from the environment.

The premold block 14 may be formed of any material that may be suitablefor ultra-low pressure molding. Exemplary materials include polyamidesand polyolefins; specific exemplary materials include MACROMELT OM 648polyamide hot melt adhesive, available from Henkel AG and Co.,Dusseldorf, Germany.

The premold block 14 illustrated herein is generally a rectangular solidand includes a plurality of bumps 16 on various surfaces thereof. Thebumps 16 may be included to provide locating features for an overlyingovermold layer 18, discussed below. Although shown as generallyrectangular, the premold block 14 may be of any shape suitable forencasing and protecting the exposed optical fibers, including cubic,ovoid, cylindrical and the like.

Referring now to FIG. 3, an assembly 20 that includes the fiber opticcable 10, the optical fiber subgroups 12, the premold block 14 (notshown in FIG. 3), and the aforementioned overmold layer 18 isillustrated therein. The overmold layer 18 is applied (i.e., molded in amold) over the premold block 14. The overmold layer 18 is typicallyapplied via low pressure (i.e., 50 to 800 psi) molding. The overmoldlayer 18 can provide an additional mechanical layer that reinforces theassembly 20, and may also provide a better aesthetic surface for theassembly 20.

The overmold layer 18 may be formed of any material that is compatiblewith the material of the premold block 14 and that is suitable for lowpressure molding. Exemplary materials include polyamides andpolyolefins. Exemplary low pressure molding materials include theaforementioned MACROMELT OM 648 polyamide.

The bumps 16 or locating features can ensure that the overmold layer 18is substantially uniform in thickness. Without the locating features,there is a tendency for the premold block 14 to be pushed to the surfaceby the molten plastic during injection. This can produce very poorsurface finish, and the possibility of fluid migration into resultantcrevasses.

The assembly 20 enjoys multiple advantages over the prior transitiontechnique discussed above. The elimination of epoxy can reduce cost,waste, and cycle times. The absence of the termination tube can alsoreduce cost and labor.

Referring now to FIG. 4, another assembly, designated broadly at 50, isshown therein. The assembly includes a first segment of a fiber opticcable 52 and a second segment of a fiber optic cable 54, wherein thefibers in the second segment 54 are housed within a furcation tube. Insome embodiments, the first segment 52 has a diameter that is slightlyhigher than the second segment 54. In this embodiment, exposed opticalfibers are protected by a low-pressure overmold of the type describedabove (not visible in FIG. 4). The overmold is then covered with anadhesive-lined heat shrink tube 58 for added abrasion- andUV-resistance.

Compared to the prior technique of reducing the diameter of a fiberoptic cable, the assembly 50 offers at least two advantages. Replacementof epoxy can reduce cost, waste, and cycle times. In addition, there isno need for a separate termination tube in addition to the furcationtube and the epoxy, which eliminates the cost of the tube itself and thelabor to install the tube.

It should also be understood that the furcation tubes 13 discussed abovemay be replaced with a cable jacket or other elongate tubular member,which may also serve the purpose of protection the fiber(s) containedtherein.

The foregoing is illustrative of the present invention and is not to beconstrued as limiting thereof. Although exemplary embodiments of thisinvention have been described, those skilled in the art will readilyappreciate that many modifications are possible in the exemplaryembodiments without materially departing from the novel teachings andadvantages of this invention. Accordingly, all such modifications areintended to be included within the scope of this invention as defined inthe claims. The invention is defined by the following claims, withequivalents of the claims to be included therein.

That which is claimed is:
 1. An assembly, comprising: a fiber optic cable comprising at least one optical fiber and a surrounding jacket; at least one elongate tubular member housing the optical fiber; wherein a gap exists between the elongate tubular member and the jacket such that the optical fiber has an exposed region; and a premold block formed of an ultra-low pressure material, the premold block encasing the exposed region of the optical fiber.
 2. The assembly defined in claim 1, further comprising an overmold layer that covers the premold block.
 3. The assembly defined in claim 1, wherein the premold material is a polymeric material selected from the group consisting of polyamide and polyolefin.
 4. The assembly defined in claim 2, wherein the premold block includes locating features to locate the premold block in a mold used to create the overmold layer.
 5. The assembly defined in claim 1, wherein the at least one optical fiber is a plurality of optical fibers, and the at least one elongate tubular member is a plurality of furcation tubes, each of the furcation tubes housing one or more of the plurality of optical fibers.
 6. An assembly, comprising: a fiber optic cable comprising at least one optical fiber and a surrounding jacket; a elongate tubular member housing the plurality of optical fibers; wherein a gap exists between the elongate tubular member and the jacket such that the optical fiber has an exposed region; and an overmold formed of a low pressure material, the overmold encasing the exposed region of the optical fiber.
 7. The assembly defined in claim 6, further comprising a heat-shrink tube that overlies the overmold.
 8. The assembly defined in claim 6, wherein the low pressure material is a polymeric material selected from the group consisting of polyamide and polyolefin.
 9. The assembly defined in claim 6, wherein the at least one optical fiber is a plurality of optical fibers, and wherein the elongate tubular member is a plurality of furcation tubes.
 10. A method for breaking out optical fibers from a fiber optic cable, comprising the steps of: (a) stripping a portion of a surrounding jacket from a fiber optic cable comprising at least one optical fiber residing within the jacket; (b) inserting the optical fiber into an elongate tubular member, wherein a gap exists between the elongate tubular member and the jacket such that the optical fiber has an exposed region; and (c) molding a premold block over the exposed region of the optical fiber at a molding pressure of between about 0 and 50 psi.
 11. The method defined in claim 10, wherein step (c) comprises molding the premold block from an ultra-low pressure material.
 12. The method defined in claim 11, wherein the premold material is a polymeric material selected from the group consisting of polyamide and polyolefin.
 13. The method defined in claim 10, further comprising the step of molding an overmold layer over the premold block.
 14. The method defined in claim 13, wherein the premold block includes locating features that assist with locating the premold block within a mold used to mold the overmold layer.
 15. The method defined in claim 10, wherein the at least one optical fibers is a plurality of optical fibers, and wherein the elongate tubular member is a plurality of furcation tubes.
 16. A method for transitioning optical fibers from a fiber optic cable into an elongate tubular member, comprising the steps of: (a) stripping a portion of a surrounding jacket from a fiber optic cable comprising at least one optical fiber residing within the jacket; (b) inserting the optical fiber into an elongate tubular member, wherein a gap exists between the elongate tubular member and the jacket such that the optical fiber has an exposed region; and (c) molding an overmold over the exposed region of the optical fibers at a molding pressure of between about 50 and 800 psi.
 17. The method defined in claim 16, further comprising the step of applying a heat-shrink tube that overlies the overmold.
 18. The method defined in claim 16, wherein the low pressure material is a polymeric material selected from the group consisting of polyamide and polyolefin.
 19. The method defined in claim 16, wherein the at least one optical fiber is a plurality of optical fibers, and wherein the elongate tubular member is a furcation tube. 